Incident occurred today at the dog park (I know spare me your opinions please). I have a 3 y/o female. Generally a good dog, not dominant in any way. We were at the park for about an hour and a half. We must have come into contact with 30-35 others dogs of all breeds and ages. No problems. My dog is not dominant at all, if anything she is a little on the submissive side. She gets along with everybody at the park. At home she's more reactive and protective, but out and about she's generally a perfect angel.

Today a lady brought another gsd to the park. A year and a half male who was taller and a little leaner than my girl, which is saying something because she's pretty large. Talking to this lady I found out that our dogs shared the same grand sire. After a period of sniffing each other and running around my dog started to go after him very aggressively something that is not in character for her. After separating them she did it again. Paying no attention to other dogs as she made a beeline straight towards him.

If anything it reminded me almost of the aggression a female can produce to a male when she is not yet ready to mate but this dog wasn't trying to mount her or anything. Both of these dogs have been fixed. I packed up and left. The dog park has been essential to both my dog and I in having a good time and we both have many friends up there. I've been thinking how odd this is. What are the odds that the one dog out of hundreds that she would show aggression to is basically her male mirror image from the same breeder and lineage? Does anyone have any ideas??